diff options
Diffstat (limited to 'Documentation/gpio')
| -rw-r--r-- | Documentation/gpio/board.txt | 10 | ||||
| -rw-r--r-- | Documentation/gpio/driver.txt | 80 | ||||
| -rw-r--r-- | Documentation/gpio/sysfs.txt | 6 |
3 files changed, 90 insertions, 6 deletions
diff --git a/Documentation/gpio/board.txt b/Documentation/gpio/board.txt index f59c43b64..309217862 100644 --- a/Documentation/gpio/board.txt +++ b/Documentation/gpio/board.txt @@ -21,8 +21,8 @@ exact way to do it depends on the GPIO controller providing the GPIOs, see the device tree bindings for your controller. GPIOs mappings are defined in the consumer device's node, in a property named -either <function>-gpios or <function>-gpio, where <function> is the function -the driver will request through gpiod_get(). For example: +<function>-gpios, where <function> is the function the driver will request +through gpiod_get(). For example: foo_device { compatible = "acme,foo"; @@ -31,9 +31,13 @@ the driver will request through gpiod_get(). For example: <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */ <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */ - power-gpio = <&gpio 1 GPIO_ACTIVE_LOW>; + power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>; }; +Properties named <function>-gpio are also considered valid and old bindings use +it but are only supported for compatibility reasons and should not be used for +newer bindings since it has been deprecated. + This property will make GPIOs 15, 16 and 17 available to the driver under the "led" function, and GPIO 1 as the "power" GPIO: diff --git a/Documentation/gpio/driver.txt b/Documentation/gpio/driver.txt index 90d0f6aba..12a61948e 100644 --- a/Documentation/gpio/driver.txt +++ b/Documentation/gpio/driver.txt @@ -62,6 +62,11 @@ Any debugfs dump method should normally ignore signals which haven't been requested as GPIOs. They can use gpiochip_is_requested(), which returns either NULL or the label associated with that GPIO when it was requested. +RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs +(like PM runtime) in its gpio_chip implementation (.get/.set and direction +control callbacks) if it is expected to call GPIO APIs from atomic context +on -RT (inside hard IRQ handlers and similar contexts). Normally this should +not be required. GPIO drivers providing IRQs --------------------------- @@ -73,6 +78,13 @@ The IRQ portions of the GPIO block are implemented using an irqchip, using the header <linux/irq.h>. So basically such a driver is utilizing two sub- systems simultaneously: gpio and irq. +RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs +(like PM runtime) as part of its irq_chip implementation on -RT. +- spinlock_t should be replaced with raw_spinlock_t [1]. +- If sleepable APIs have to be used, these can be done from the .irq_bus_lock() + and .irq_bus_unlock() callbacks, as these are the only slowpath callbacks + on an irqchip. Create the callbacks if needed [2]. + GPIO irqchips usually fall in one of two categories: * CHAINED GPIO irqchips: these are usually the type that is embedded on @@ -93,6 +105,38 @@ GPIO irqchips usually fall in one of two categories: Chained GPIO irqchips typically can NOT set the .can_sleep flag on struct gpio_chip, as everything happens directly in the callbacks. + RT_FULL: Note, chained IRQ handlers will not be forced threaded on -RT. + As result, spinlock_t or any sleepable APIs (like PM runtime) can't be used + in chained IRQ handler. + if required (and if it can't be converted to the nested threaded GPIO irqchip) + - chained IRQ handler can be converted to generic irq handler and this way + it will be threaded IRQ handler on -RT and hard IRQ handler on non-RT + (for example, see [3]). + Know W/A: The generic_handle_irq() is expected to be called with IRQ disabled, + so IRQ core will complain if it will be called from IRQ handler wich is forced + thread. The "fake?" raw lock can be used to W/A this problem: + + raw_spinlock_t wa_lock; + static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) + unsigned long wa_lock_flags; + raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags); + generic_handle_irq(irq_find_mapping(bank->chip.irqdomain, bit)); + raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags); + +* GENERIC CHAINED GPIO irqchips: these are the same as "CHAINED GPIO irqchips", + but chained IRQ handlers are not used. Instead GPIO IRQs dispatching is + performed by generic IRQ handler which is configured using request_irq(). + The GPIO irqchip will then end up calling something like this sequence in + its interrupt handler: + + static irqreturn_t gpio_rcar_irq_handler(int irq, void *dev_id) + for each detected GPIO IRQ + generic_handle_irq(...); + + RT_FULL: Such kind of handlers will be forced threaded on -RT, as result IRQ + core will complain that generic_handle_irq() is called with IRQ enabled and + the same W/A as for "CHAINED GPIO irqchips" can be applied. + * NESTED THREADED GPIO irqchips: these are off-chip GPIO expanders and any other GPIO irqchip residing on the other side of a sleeping bus. Of course such drivers that need slow bus traffic to read out IRQ status and similar, @@ -133,6 +177,13 @@ To use the helpers please keep the following in mind: the irqchip can initialize. E.g. .dev and .can_sleep shall be set up properly. +- Nominally set all handlers to handle_bad_irq() in the setup call and pass + handle_bad_irq() as flow handler parameter in gpiochip_irqchip_add() if it is + expected for GPIO driver that irqchip .set_type() callback have to be called + before using/enabling GPIO IRQ. Then set the handler to handle_level_irq() + and/or handle_edge_irq() in the irqchip .set_type() callback depending on + what your controller supports. + It is legal for any IRQ consumer to request an IRQ from any irqchip no matter if that is a combined GPIO+IRQ driver. The basic premise is that gpio_chip and irq_chip are orthogonal, and offering their services independent of each @@ -169,6 +220,31 @@ When implementing an irqchip inside a GPIO driver, these two functions should typically be called in the .startup() and .shutdown() callbacks from the irqchip. +Real-Time compliance for GPIO IRQ chips +--------------------------------------- + +Any provider of irqchips needs to be carefully tailored to support Real Time +preemption. It is desireable that all irqchips in the GPIO subsystem keep this +in mind and does the proper testing to assure they are real time-enabled. +So, pay attention on above " RT_FULL:" notes, please. +The following is a checklist to follow when preparing a driver for real +time-compliance: + +- ensure spinlock_t is not used as part irq_chip implementation; +- ensure that sleepable APIs are not used as part irq_chip implementation. + If sleepable APIs have to be used, these can be done from the .irq_bus_lock() + and .irq_bus_unlock() callbacks; +- Chained GPIO irqchips: ensure spinlock_t or any sleepable APIs are not used + from chained IRQ handler; +- Generic chained GPIO irqchips: take care about generic_handle_irq() calls and + apply corresponding W/A; +- Chained GPIO irqchips: get rid of chained IRQ handler and use generic irq + handler if possible :) +- regmap_mmio: Sry, but you are in trouble :( if MMIO regmap is used as for + GPIO IRQ chip implementation; +- Test your driver with the appropriate in-kernel real time test cases for both + level and edge IRQs. + Requesting self-owned GPIO pins ------------------------------- @@ -190,3 +266,7 @@ gpiochip_free_own_desc(). These functions must be used with care since they do not affect module use count. Do not use the functions to request gpio descriptors not owned by the calling driver. + +[1] http://www.spinics.net/lists/linux-omap/msg120425.html +[2] https://lkml.org/lkml/2015/9/25/494 +[3] https://lkml.org/lkml/2015/9/25/495 diff --git a/Documentation/gpio/sysfs.txt b/Documentation/gpio/sysfs.txt index 0700b5563..aeab01aa4 100644 --- a/Documentation/gpio/sysfs.txt +++ b/Documentation/gpio/sysfs.txt @@ -20,14 +20,14 @@ userspace GPIO can be used to determine system configuration data that standard kernels won't know about. And for some tasks, simple userspace GPIO drivers could be all that the system really needs. -DO NOT ABUSE SYFS TO CONTROL HARDWARE THAT HAS PROPER KERNEL DRIVERS. +DO NOT ABUSE SYSFS TO CONTROL HARDWARE THAT HAS PROPER KERNEL DRIVERS. PLEASE READ THE DOCUMENT NAMED "drivers-on-gpio.txt" IN THIS DOCUMENTATION DIRECTORY TO AVOID REINVENTING KERNEL WHEELS IN USERSPACE. I MEAN IT. REALLY. Paths in Sysfs -------------- -There are three kinds of entry in /sys/class/gpio: +There are three kinds of entries in /sys/class/gpio: - Control interfaces used to get userspace control over GPIOs; @@ -106,7 +106,7 @@ read-only attributes: "label" ... provided for diagnostics (not always unique) - "ngpio" ... how many GPIOs this manges (N to N + ngpio - 1) + "ngpio" ... how many GPIOs this manages (N to N + ngpio - 1) Board documentation should in most cases cover what GPIOs are used for what purposes. However, those numbers are not always stable; GPIOs on |